Submitted to: Soil and Crop Science Society of Florida Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 6/1/2001
Publication Date: N/A
Interpretive Summary: Soybean is especially beneficial in many cropping systems because it fixes nitrogen from the atmosphere and does not require nitrogen fertilizer. However, the nitrogen fixation process is generally quite sensitive to soil drying. One cultivar, Jackson, was previously discovered to have nitrogen fixation that was tolerant to water-deficit conditions. Oxygen permeability into the root nodules is intimately involved in the regulation of nodule activity and the oxygen permeability of the nodules of Jackson appears to be unusually low. A field experiment involving an ARS-USDA scientist located at the Center for Medical, Agricultural and Veterinary Entomology, Gainesville, FL, was designed to artificially induce a lowered oxygen permeability to test the importance of a decreased permeability for drought tolerance. The results of this experiment confirmed that a lowered oxygen permeability was advantageous in ameliorating the effects of soil drying on nitrogen fixation activity.
Technical Abstract: N2 fixation in soybean (Glycine max, Merr.) is especially sensitive to soil drying even at relatively high water contents. One possible physiological explanation for this sensitivity is that O2 permeability of nodules is associated with N2 fixation response to soil water deficit. Two cultivars of soybean, with different levels of N2 fixation drought tolerance, were grown in the field, and subjected to water deficit treatment during vegetative growth. To test the interaction of O2 limitation and water deficit on N2 fixation, nodule permeability of well-watered and drought-stressed plants was decreased by enriching the rhizosphere with O2, and the effects were measured on the response of plant mass accumulation. The results of this experiment indicated that the elevated O2 helped to sustain N2 fixation with drying soils, and that drought tolerance of N2 fixation may be partly associated with decreased nodule permeability to O2. However, after 8 d of drought- stress treatment, increasing external O2 failed to result in any recovery of nodule N2 fixation activity from drought stress, in either soybean cultivar.